Having the security PIN enabled with your SIM card, it gives you additional protection from unauthorized use. Your phone will ask you to enter the SIM PIN every time you turn your phone on. Below are the steps on how to enable the SIM PIN with Samsung Galaxy S3.

Remember that this is different from phone lock code or pattern.

Go to Apps

Tap on Settings

Tap on Security

Tap on Setup SIM card lock

Tap on the box beside Lock SIM card to enable and disable it

It will then ask to enter your current PIN and tap OK.

Note: When you failed to enter the correct PIN three times in a row, your phone will ask to enter the PUK. If you don't know what it is, you might have to contact your customer service to obtain that. When incorrect PUK was entered for more than 10 times in a row, the SIM card will be blocked permanently.